Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$152.94	7.569%	$164.516	$164.52	$164.50	$164.50
Purchase #2	$80.93	13.720%	$92.0336	$92.03	$92.05	$92.00
Purchase #3	$228.74	6.243%	$243.0202	$243.02	$243.00	$243.00
Purchase #4	$56.92	7.832%	$61.378	$61.38	$61.40	$61.40
Purchase #5	$246.95	13.487%	$280.2561	$280.26	$280.25	$280.30
Purchase #6	$108.60	9.183%	$118.5727	$118.57	$118.55	$118.60
Purchase #7	$145.31	11.746%	$162.3781	$162.38	$162.40	$162.40
7 purchase totals =	$1,020.39		$1,122.1547	$1,122.16	$1,122.15	$1,122.20